Clinical utility of ADAMTS-13 testing in suspected thrombotic microangiopathy: an audit of ADAMTS-13 activity assay requests in routine practice from a tertiary hospital

Aims: Differentiation between thrombotic thrombocytopenic purpura (TTP) and other microangiopathic haemolytic anaemia (MAHA) processes can be difficult. Since the documentation of ADAMTS-13 deficiency in TTP, several ADAMTS-13 activity assays have been developed for use in the diagnosis of TTP and/or other microangiopathic disorders. We reviewed the clinical utility of ADAMTS-13 activity testing in suspected TTP, as used in routine clinical practice in a tertiary referral hospital. Methods: All requests for ADAMTS-13 activity levels performed at our institution after introduction of the assay were retrospectively audited with respect to clinical diagnosis and results. Results: In total 57 individual patients were tested, of whom only 46% had a MAHA process. Severe ADAMTS-13 deficiency was present in five TTP patients and in one patient with fulminant hepatic failure. Conclusions: Our experience suggests that severely reduced levels are relatively specific for TTP, but may also occur in fulminant hepatic failure. Patients without MAHA may have reduced ADAMTS-13 activity and there is significant overlap in the range of ADAMTS-13 activity seen in non-TTP MAHA diagnoses. This supports the observation that outside the diagnosis and (possible) follow-up of suspected idiopathic TTP, the ADAMTS-13 activity assay has limited clinical utility. Further education about the role of ADAMTS-13 activity testing is needed.